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Old 1st October 2012, 03:55 AM   #1101
NEO Dan is offline NEO Dan  United States
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When you cal the REW SPL meter you need to actually hook up the cab to the amp and the mic to the soundcard, you can't just use the loopback. Raise or lower the mic input gain until you are in the 120-130dB max level area.
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Old 1st October 2012, 04:02 AM   #1102
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Quote:
Originally Posted by NEO Dan View Post
When you cal the REW SPL meter you need to actually hook up the cab to the amp and the mic to the soundcard, you can't just use the loopback.
They were


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Raise or lower the mic input gain until you are in the 120-130dB max level area.
I'll try this. Hopefully, that test start to audio delay problem will magically disappear.
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Old 1st October 2012, 04:09 AM   #1103
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What I don't get is how your levels on the input side could "go up" before you hear the sweep? This would indicate a monitor loop is on or wrong input/channel selection...

You could disconnect all the inputs and outputs and try to measure if the input meters go up you have an internal signal routing problem...
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Old 1st October 2012, 04:32 AM   #1104
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What I don't get is how your levels on the input side could "go up" before you hear the sweep?
I don't believe I said they did..
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Old 1st October 2012, 04:55 AM   #1105
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Originally Posted by CRESCENDO View Post
I don't believe I said they did..
I misunderstood:
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Still, when I go in to measure, I click "Check Levels" there, it pops up the "Signal too Low" warning before any audio is played. Then, audio plays for a couple seconds and stops (same happens w/measurement sweep). Maybe I should set up a loop for REW to calculate for sound card delay option.
Are you running the REW beta code or something?

Latency thoughts.
If your SC bitrate is externally/manually set to a higher rate than REW you will fill the buffer before the impulse gets there so make sure 44.1 is set for the card and REW.
You may want to increase buffer sizes in REW prefs but I get by just fine on 32k.
Notice my card inverts polarity...
Click the image to open in full size.

First objective for me would be to get the system measuring correctly with the loop back cable just after the calibration. Look at the impulse, polarity invert if necessary using check box in controls (upper right corner). The FR should be basically flat because you already have the calibration file in place.

Click the image to open in full size.
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Old 1st October 2012, 05:09 AM   #1106
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Originally Posted by NEO Dan View Post
I misunderstood:
Yeah, levels don't go up until I hear audio (mic "hears" audio, too). I get that Low Level warning before I hear audio. Maybe it IS a latency thing..


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Are you running the REW beta code or something?
Not that I know of - I didn't even know about it.


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Originally Posted by NEO Dan View Post
Latency thoughts.
If your SC bitrate is externally/manually set to a higher rate than REW you will fill the buffer before the impulse gets there so make sure 44.1 is set for the card and REW.
They're both set to 48k. I can try 44.1k next time.


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You may want to increase buffer sizes in REW prefs but I get by just fine on 32k.
I currently have them set to 128k.


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Notice my card inverts polarity...
Click the image to open in full size.

First objective for me would be to get the system measuring correctly with the loop back cable just after the calibration. Look at the impulse, polarity invert if necessary using check box in controls (upper right corner). The FR should be basically flat because you already have the calibration file in place.

Click the image to open in full size.
I'll try taking a measurement with the loop back cable and see what happens. Thanks for your help.
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Old 1st October 2012, 05:13 AM   #1107
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128k looks even better:
Click the image to open in full size.
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Old 1st October 2012, 05:45 AM   #1108
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Looking at REW "support" forum I see:
Quote:
On the V5 Soundcard Preferences tick the "Force Big-Endian" box and see if that helps.
And then then JohnM goes on to say:
9/10/12 Link
Quote:
Unfortunately Apple's Java runtime has a bug that prevents Java applications accessing the inputs of multichannel soundcards (anything with more than a single stereo input). If your iMac has on-board line in and out that should work fine, though. Failing that the problem might not be present in Oracle's OpenJDK version of Java for OS X, Oracle Releases New Java Updates - Java SE 7 Update 6, JavaFX 2.2 and JavaFX Scene Builder 1.0, although I think Apple contributed code towards the project so they may have generously donated their bugs at the same time
And back in 09' I see a claim from a user that Apple Java could not access Firewire sound device inputs...

I'd get rid of everything but the Firewire box and the Loopback cable and sort it out. Take a screen shot of the scope and save the REW file if it appears to be working, and we can go from there...
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Old 1st October 2012, 12:55 PM   #1109
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Hi Crescendo,
I watched 3 you tube vids that were very helpful with setting up the mic and sound card,
Room EQ Wizard - Step 1 - Calibration - YouTube
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NS
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Old 1st October 2012, 06:26 PM   #1110
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Yeah, I don't think we've ever had a gig with anything but 120V (15A or 20A) - with the exception of one gig last year off an MQ Power Whisperwatt generator.
So, I think I'd be more comfortable with 120V amps. I would, however, like to further educate myself on different power configurations (3 phase included) should the opportunity/conditions arise.
Unlike the PLX series, the QSC PL380 is also a good LF amp.

Most USA smaller venues use single phase power, two "hot" legs of 120 volts, 240 volts AC between the two legs. Power transformers have changed over the years, older transformers encountered may be 220-230 volts between legs.

Three phase power has three hot legs of 120 volts, nominally only 208 volts between them. The phase angle between the three legs allows the use of three phase motors, which won't run on single phase.

Back when I owned chain motors, had four single phase 120 volt hoists for certain venues lacking three phase, and a dozen 3 phase motors for "normal" concert venues.
When lifting a ton, the 120V chain motors drew near 20 amps, 10 or 12 AWG was needed for a 100 foot run or they would not pull the weight, while three of the same CM 3 phase motors could run on a 20 amp circuit using 14 gauge and not stall, even when slipping the protective clutch plates which slip above a 1 ton load. Two ton CM motors use the same motor/clutch, but twice the chain over a sheave to gain double the mechanical advantage.
Riggers hate pulling up 80 feet of doubled chain...

Some older three phase installations have a "wild leg" which can fluctuate wildly depending on the load on the three phases, won't damage a motor, but can fry gear when voltage on the "wild leg" drops to 60, or rises to 180 V. I hate it when that happens..

One problem with "old school" (non-switching power supply) amplifiers rated for "220" volts (ostensibly they can run off 208-240 volts) is the 208 volts between two hot legs of a three phase service may not allow full rated power from the amp. Some amps have different transformer taps to deal with the different voltages available, while many modern PSU designs deal with voltage change automatically.

One last observation, although an outlet may read 120 VAC when unloaded, different amp designs will “brown out” (dropping to 110V or even less) the service on peaks to a different degree, some amps that perform just fine on bench regulated 120V power don’t behave at all well in the real world of lower voltage at higher amperage peaks.

Sometimes the weight savings afforded in a switching PSU amp are completely offset by the heavier AWG cable needed to keep the voltage up, and the amp performing to spec.

Art Welter
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